The present disclosure generally relates to semiconductor devices, and particularly to semiconductor structures including field effect transistors having multiple effective work functions, and methods of manufacturing the same.
Advanced semiconductor circuits employ multiple types of field effect transistors having different threshold voltages. While methods of employing ion implantation to alter the channel doping for the purpose of providing different threshold voltages are known in the art, control of threshold voltages through ion implantation alone does not provide a full range of variations in the threshold voltage that is desired from field effect transistors. Thus, an integration scheme is desired that can provide a wider range of threshold voltages for various field effect transistors.